1. Universidad Nacional de Colombia- sede Palmira, Carrera 32, Chapinero, Palmira, Colombia
2. Centro Internacional de Agricultura Tropical (CIAT), A.A 6713, Cali, Colombia
3. International Atomic Energy Agency (IAEA), VIC, PO Box 100, 1400 Vienna, Austria
4. Present address: Plant Polymer Research Unit, National Center for Agricultural Utilization Agricultural Research Service, United States Department of Agriculture, 1815 North University Street, Peoria, IL 61604, USA